1. Field of the Invention
The present invention relates to an improvement of developers for diazo copying materials, and particularly it relates to a liquid developer for use in developing binary diazo copying materials which consists essentially of an alkali metal salt of an aminoacid or an alkaline earth metal salt of an aminoacid or both of these salts.
2. Description of the Prior Art
As the prevalent method of developing binary diazo copying materials, there are the so-called wet process, dry process, thermal process and semi-dry process. Among these processes, the wet process is a method wherein the developing is performed by impregnating or coating a diazo copying material with a developer consisting essentially of an inorganic or organic alkaline compound. The dry process is a method wherein a diazo copying material is treated with, for instance, ammonia gas thereby effecting color development. And, the thermal process is a method wherein a photosensitive material prepared by coating a mixture consisting of a diazo compound, a coupler and an alkali-generating agent on a support is subjected to heating thereby generating alkali and effecting color development.
However, all of these conventional developing methods have various drawbacks such as follows.
(1) In the case of the wet process, water contained in the developer evaporates gradually to cause crystallization of the alkali ingredient of the developer or coloring of the developer in a long period of time thereby rendering it impossible to obtain a clear-cut copy stably at all times. Besides, depending on the kind of alkaline compound constituting the developer for use therein, there are instances where a loathsome offensive smell is given out. PA1 (2) In the case of the dry process, because of the employment of ammonia for the developer, the very strong smell of ammonia poses a problem from the view point of environment sanitation. Besides, it requires a large-scale and expensive developing apparatus. PA1 (3) In the case of the thermal process, because of the presence of a substance capable of thermally generating alkali within the photosensitive layer, the preservability of the photosensitive material inevitably is deteriorated.
As a measure for making up for the foregoing drawbacks of the prior art, a developer comprising an organic amine has been proposed (cf. Japanese Patent Publication No. 23515/1970). This developer makes it possible to perform the developing by just making a modicum of said developer adhere to the photosensitive layer surface of a binary diazo copying material, and therefore the developing method employing this developer deserves the name of `semi-dry process`. However, even this semi-dry process is defective because the degree of coloring of said organic amine is so great that a conspicuous discoloring and fading of the resulting copy after development is inevitable. Moreover, the developer, when used for a long time, assumes a brown color, causing discoloring of the background of.
In this connection, as a means of overcoming the foregoing demerits of a developer employing organic amine, there have admittedly been proposed a variety of developers comprising some water-soluble alkali metal salt of carboxylic acid, water-soluble alkaline earth metal salt of carboxylic acid or water-soluble pyrolizable ammonium salt together with said organic amine (cf. Japanese Laid-open Application No. 24735/1973; Japanese Laid-open Application No. 60621/1973; Japanese Laid-open Application No. 60633/1973). However, as a matter of fact, all of these developers are defective in that they require a process of heating and drying, they give out an unpleasant smell at the time of thus drying, and they fail to produce a satisfactory copied image when used for a long time because of separation of the foregoing substances on account of the employment of water as diluent, and therefore they are still insufficient for practical use.